"Less competitive specialties". Please be aware that what may be not-competitive in the civilian world is not the same as the military match. For Navy pediatrics, for example, there were 30 people who applied this year for 14 spots, and they did not grant any civilian deferments for peds . Meaning that for the >50% of people who applied who did not match pediatrics, they were not allowed to apply to civilian pediatric programs. They were given another specialty. Civilian match rate for pediatrics is in the upper 90's%, but is one of the most competitive specialties in the military (<50% this year).
For the Match process, The Navy requires everyone rank 2 specialties that they would like to apply to (and can rank as many programs inside each specialty). They also require everyone to apply to ERAS, so that people who don't match any programs in their #1 ranked Navy specialty, #2 ranked Navy specialty, and no other spots were available in any Navy residency, they should plan on having a back-up in the civilian match. However, they will work their hardest to make sure the Navy has all of its spots filled before it grants a deferment because you did not have a good enough application to match into the military specialty of your choice. If you rank dermatology and pediatrics as your #1 and #2, and you don't match into either and neither specialty has civilian deferment spots, you may find yourself in a random spot in another specialty that has an opening.
The nice thing about the Navy is that if you fail to match into your specialty of choice for intern year, you can go do a GMO and reapply and have almost a guaranteed spot in the specialty of your choice when you come back. Or you can do GMO and get out and apply to civilian residency where you will also have a good chance of matching into your specialty of choice. So its not the end of the world if you don't match into what you want initially.